Doctors are doing research to find out what happens physically when people _________ smoking.
The moment I completed the 3000-meter race in the school sports meet, my legs _______.
_______ difficult and challenging the task may be, we must finish it on time, because there is a possibility _______our work will go down in history.
He bought a house,___________ the price is reasonable.
In the reading room, we found her ________ at a desk, with her attention ________ on a book.
All those second-hand cars are sold atbefore